The present invention relates to microwave reflector antenna and, more specifically, to microwave reflector antenna that rotate about both an azimuth axis and an elevation axis.
Microwave reflector antennas can be used in a variety of applications. For example, microwave reflector antennas can be used on an aircraft to allow the aircraft to communicate with other parties. When a microwave reflector antenna is used on an aircraft, the microwave reflector antenna is typically positioned on the crown of the exterior of the aircraft. The positioning of the microwave reflector antenna on the exterior of the aircraft increases the drag of the aircraft as it travels through the atmosphere and could expose the microwave reflector antenna to the harsh environment that the aircraft is exposed to. Therefore, the microwave reflector antennas are typically covered by a radome which completely covers the microwave reflector antenna and reduces the drag caused by positioning the microwave reflector antenna on the exterior of the aircraft.
The radome is designed to cover the microwave reflector antenna and to reduce the drag on the aircraft caused by the microwave reflector antenna. To achieve a reduction in the drag on the aircraft associated with covering a microwave reflector antenna with a radome, the radome is gradually tapered from its peak to its ends. The typical radome will have a length along the aircraft of approximately 10 to 12 inches for every inch of height for which the radome must extend above the aircraft to cover the microwave reflector antenna. The typical microwave reflector antenna requires a radome of approximately 10 to 12 feet or more in length to cover the microwave reflector antenna.
Because the cost of the radome is proportional to the size of the radome, any reduction in the height or size of the radome and the resulting length of the radome will result in a cost savings. Additionally, a decrease in the size of the radome will also decrease the drag caused by the radome on the aircraft. Therefore, it is desirable to reduce the size of the microwave reflector antenna so that the size of the radome can also be reduced.
The typical microwave reflector antenna has a reflector that is capable of rotating about two different axes. The first axis of rotation is the azimuth axis. Rotation of the reflector about the azimuth axis allows the reflector to rotate 360xc2x0 so that the reflector can point in any direction along the horizon. The second axis of rotation is the elevation axis. Rotation of the reflector about the elevation axis allows the elevation of the reflector to be adjusted so that the reflector can be orientated between the horizon and the sky.
The typical microwave reflector antenna has a stationary or base plate that is attached to the aircraft and remains stationary relative to the aircraft. A rotary plate rotates relative to the stationary plate about the azimuth axis. The reflector of the microwave reflector antenna is connected to the rotary plate so that rotation of the rotary plate about the azimuth axis causes the reflector to rotate about the azimuth axis. The reflector is typically connected to the rotary plate by elevation bearings that allow the reflector to rotate about the elevation axis. The elevation bearings are typically located on opposite peripheral sides of the reflector antenna so that the reflector antenna is positioned between a pair of elevation bearings.
The rotation of the microwave reflector antenna about both the azimuth axis and the elevation axis define a swept volume of the microwave reflector antenna through which the microwave reflector antenna must be able to freely move in order for the microwave reflector antenna to operate correctly. That is, the swept volume of the microwave reflector antenna represents the volume of space that allows all the components of the microwave reflector antenna to operate throughout their entire range of motion. Therefore, a radome designed to cover the microwave reflector antenna must not interfere with or encroach upon the swept volume of the microwave reflector antenna.
The individual component of the microwave reflector antenna which encompasses the largest volume of the swept volume of the microwave reflector antenna is the reflector. The reflector swept volume should represent the minimum swept volume that can be attained for the microwave reflector antenna. That is, if each of the other components of the microwave reflector antenna can be positioned so that the swept volume of each of the other components is within the swept volume of the reflector, the swept volume of the reflector would be the same as the swept volume of the microwave reflector antenna. Therefore, in order to reduce the swept volume of the microwave. reflector antenna and the associated size of the radome, it is desirable to position the components of the microwave reflector antenna so that the swept volume of the components are within the swept volume of the reflector.
The elevation bearings are typically located on the periphery of the reflector. Because the elevation bearings are located on the periphery of the reflector, the elevation bearings are not within the reflector swept volume and therefore increase the swept volume of the microwave reflector antenna. The elevation bearings thereby require the radome to encompass a swept volume that is larger than the reflector swept volume. Therefore, it is desirable to locate the elevational bearings within the reflector swept volume so that the elevational bearings do not cause the microwave reflector antenna swept volume to be larger than the reflector swept volume.
Therefore, what is needed is a microwave reflector antenna that has as many of its components as possible to be within the reflector swept volume so that the microwave reflector antenna swept volume is minimized. The minimization of the microwave reflector antenna swept volume allows for a smaller radome and an associated savings in cost and drag on the aircraft.
The microwave reflector antenna of the present invention is designed with a reduced swept volume so that a radome covering the microwave reflector antenna can be of minimal size.
The reduced swept volume microwave reflector antenna of the present invention generally comprises a rotary plate that is capable of being rotated about an azimuth axis. At least one elevation cradle is attached to the rotary plate so that rotation of the rotary plate about the azimuth axis causes the at least one cradle to rotate about the azimuth axis. A reflector is connected to the at least one cradle and travels along the at least one cradle as the reflector rotates about an elevation axis. The reflector also rotates about the azimuth axis with the rotation of the at least one cradle about the azimuth axis. The rotation of the reflector about the azimuth axis and about the elevation axis define a swept volume of the reflector. The at least one cradle is positioned on the rotary plate so that the at least one cradle is within the swept volume of the reflector. The positioning of the at least one cradle within the swept volume of the reflector prevents the at least one cradle from causing the swept volume of the microwave reflector antenna to be larger than the reflector swept volume.
In another aspect of the present invention, a microwave reflector antenna with a reduced swept volume has a rotary plate that is capable of rotating about an azimuth axis. At least one elevation cradle is attached to the rotary plate so that rotation of the rotary plate about the azimuth axis causes the at least one cradle to rotate about the azimuth axis. The at least one cradle has a curved guide. The curved guide has a plurality of ball bearings. A reflector having front and back surfaces is capable of rotating about an elevation axis. A portion of the front surface of the reflector is concave and reflects microwave energy. At least one track is attached to the back surface of the reflector. The at least one track is positioned in and travels through the guide on the at least one cradle as the reflector rotates about the elevation axis. The reflector rotates about the azimuth axis with the rotation of the at least one cradle about the azimuth axis. The rotation of the reflector about the azimuth axis and about the elevation axis define a swept volume of the reflector. The at least one cradle is positioned on the rotary plate so that the at least one cradle is within the swept volume of the reflector. The positioning of the at least one cradle within the swept volume of the reflector prevents the at least one cradle from causing the swept volume of the microwave reflector antenna to be larger than the swept volume of the reflector.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.